Bottom Line:
The recovery is over 85% of spiked Lp SG 1 cells in 1 l of tap water and detection limits are around 50 and 15 cells per litre for total and viable Lp, respectively.In 53% of the water samples from different taps and showers significantly higher concentrations of Lp were detected by flow cytometry.No correlation to the plate culture method was found.

f2: Examples for green versus blue fluorescence dot plots for different tap water samples. (A) shows quantification in spiked tap water and (B) is the corresponding negative control. (C–F) show different positive tap water samples with naturally occurring Lp cells. (D–F) indicate that environmental Lp cells may be smaller in some cases and display less fluorescence than spiked Lp cells grown in liquid culture. The complete FCM output for these examples can be found in Figs S1–S5, except for (C), which is from Fig. 6.

Mentions:
Since we demonstrated previously that Lp quantification by FCM and IFM agree very well (Füchslin et al., 2010), the spiking counts were determined by FCM. When applying our gating approach for spiked tap water samples it was possible to discriminate Lp cells very well from background signals in the main fluorescence dot plots, i.e., green versus blue fluorescence; the negative controls contained very few background noise events (Fig. 2A and B, and supporting data in Figs S1 and S2). Background noise events (false positives) for total and viable Lp were 26.0 ± 8.0 and 8.0 ± 2.5 events l−1 (n = 15), respectively.

f2: Examples for green versus blue fluorescence dot plots for different tap water samples. (A) shows quantification in spiked tap water and (B) is the corresponding negative control. (C–F) show different positive tap water samples with naturally occurring Lp cells. (D–F) indicate that environmental Lp cells may be smaller in some cases and display less fluorescence than spiked Lp cells grown in liquid culture. The complete FCM output for these examples can be found in Figs S1–S5, except for (C), which is from Fig. 6.

Mentions:
Since we demonstrated previously that Lp quantification by FCM and IFM agree very well (Füchslin et al., 2010), the spiking counts were determined by FCM. When applying our gating approach for spiked tap water samples it was possible to discriminate Lp cells very well from background signals in the main fluorescence dot plots, i.e., green versus blue fluorescence; the negative controls contained very few background noise events (Fig. 2A and B, and supporting data in Figs S1 and S2). Background noise events (false positives) for total and viable Lp were 26.0 ± 8.0 and 8.0 ± 2.5 events l−1 (n = 15), respectively.

Bottom Line:
The recovery is over 85% of spiked Lp SG 1 cells in 1 l of tap water and detection limits are around 50 and 15 cells per litre for total and viable Lp, respectively.In 53% of the water samples from different taps and showers significantly higher concentrations of Lp were detected by flow cytometry.No correlation to the plate culture method was found.